drop table machine_a;

create table machine_a(
	machine_no number  primary key,
 	component_id number,
 	working_start varchar2(30),
 	working_end varchar2(30),
 	is_fault varchar(1),
 	constraint a_component_code_fk foreign key(component_id) REFERENCES component(component_id)
);

select machineA.nextval from dual

drop sequence machineA

select machineA1.nextval from dual

drop sequence machineA1;

create sequence machineA1;

create sequence machineA;

delete from MACHINE_A;
delete from MACHINE_B;
delete from MACHINE_C;
delete from HISTORY;

select * from MACHINE_A;
select * from MACHINE_B;
select * from MACHINE_C;

select * from HISTORY;
select * from product;
select * from COMPONENT;